Coating method and apparatus



Sept l945.- w. F. GRUPE COATING METHOD AND APPARATUS Filed April 15,1941 R WY 0 E fim m W 0 N w Is A W set of the Patented Sept. 4, 1945UNIT-E STATES PATEN 2,388,964 COATING METHOD AND APBARATUS William F.Grupe, Lyndhurst, N. 3., assignor to Inter-chemical Corporation, New

corporation of Ohio York, N. E, a

Application April 15, 1941, Serial No. 388,573

.6 Claims.

This lnyention relates to the art of coating metal and aims to providean improved method and apparatus by means of which metal, in the form ofa thin continuous strip, may be effectively covered, preferably on bothsides thereof, with a' throughout its length and width. Some of theunevenness in the stock may be caused by improper camber in the rollingmills; or if a particular strip which is to be coated has been cut fromone of greater width, the edge or edges-which have been out are usuallywavy or scalloped due to too deep a set of the slitter knives, the pitchof the waves or scallops varying with the depth of blade. Moreover, thecut edges are often blurred. When attempts are made to coat such stripmetal with apparatus now available,

it is usually not possible to overcome the unevenness or tendency totwist with the tensions that are applied in normal coatin apparatus.This creates at least two important difliculties in the coatingoperation: first, it is not possible to obtain a uniform thickness ofcoat throughout the width of the strip: and second,.the scalloped andburred edge actually cuts into the usual resilient surfaced coatingrollers, particularly when a reverse roll coater is employed. While thislatter trouble is primarily one which involves the coating apparatus, itwill be understood that any appreciable cutting into the coating rollerswill ultimately alfect the coating operation. Furthermore, be-' cause ofthe relatively large diameters of the usual coating rollers, the coatingtends to form streaks or ridges which are particularly pronounced whenthe coating material is pigmented. These and other difficulties havebeen of such a nature that there are not any available commercialmachines or methods for properly coating thin strip metal,

coating is applied to both sides of the metal web,

two small diameter bars are employed and arranged so that the anglebetween the plane in which the strip is being fed and a plane passingthrough centers of the bars is between 3 and 30. The coated strip isfirst broken over one bar which levels and regulates the thickness ofthe layer on one side, .and is then bent back by breaking over thesecond bar which levels and regulates the thickness of the layer on theother side. By proceeding'in this manner, both sides of a wavy stripsuch as is used for manufacturing food containers and the like.

According to my invention, the strip metal to be coated and undersuitable tension is covered on one side with an excess of the desiredcoating material and is then bent transversely at an angle of from about3 .to 30 by breaking the strip over a bar of very smal diameter which ispositioned along the line of the bend and is constructed and arranged sothat the coating, throughout the entire width of the strip, is leveledto a uniform layer freeof ridges and all excess coating is re- 7 movedas the strip passe there'over. Where the coated on both sides thereofwith desired coating material. Said of metal may be continuously coatedthroughout the width of the strip with a uniform and resulated layer ofcoating material free from all streaks, ridges or unevenness.

The above and other features and objects of the invention will becomeapparent on consideration of the following detailed description and theacc'ompanying drawing, in which;

Fig. 1 is a diagrammatic elevational view of an apparatus forcontinuously coating strip metal in which the apparatus features of myinvention have been embodied; and

Fig. 2 is a fragmentary perspective detail view, with certain dimensionsexaggerated for the sake of clarity, of one form of bar for bending astrip and leveling and upon one side thereof.

Referring now to the drawing, it will be observed that-a strip of thingauge metal 5 is fed from a suitable supply reel or coil 6 upwardly overa feed or guide roll "i into a cleaning chambar 8. This cleaning chamberb may be of any conventional construction and contains some material,such as trlchlorethylene, for cleaning the strip 5 as it passestherethrough over a large glllding drum It and upwardly to a secondguiding roller II. From the roller II, the strip passes downwardly andaround a guide roller I 2 to a pair of brake rollers l3 and It. Theserollers are of a rather large diameter and cause the strip to beflattened out somewhat in passing around them in the path shown inFig. 1. The strip .is then fed in a substantially horizontal paththrough a coating apparatus, which is designated as a whole by thereference numeral it, where it is passed through a heating chamber Itfor drying the applied coating, a cooling chamber I1 and into a pull andfeed apparatus which includes rollers It, 20, 2! and 22 that are drivenand arranged to grip the metal sufficiently to feed or pull it throughthe entire apparatus. The web or strip 5; maybe passed from theuppermost roller 22 to regulating the coating applieda layer of anystripis next a rewind reel 23, or it may be cut into sheets'in anyconventional manner, if desired.

In one form of coating apparatus that has been tried, the strip 5extends in a horizontal path from the upper brake roller M to thelowermost roller iii of the feed and pull apparatus and is substantiallyunsupported throughout this distance. The braking power of the rubbercovered braking rollers 13 and i 4 is used to Provide a sufficientresistance for maintaining the supported strip taut and in a horizontalplane; and sumcient tension is provided to cause the strip to be inproper position for coating. However, due to the fact that the stripmetal is usually not fiat, because of conditions'encountered in itsmanufacture, and has at least one sharp and scalloped edge, difficultiesare encountered in the coating operation.

Where the strip metal is to be used in the manufacture of containers, itis desirable to provide a thin coat of protective material that isentirely continuous, free of porosity, and of uniform protective valueover the entire surface of the metal. Such coated stock is then formedinto cans or containers and during fabrication may be bent either ineasy turns or sharply in crimping and closing the side seams for thecontainers; or it may be shaped and drawn, as in making the can endswhen sharp draws are made which actually distort the metal. Some of thefabricating operations cause the strip to be bent 180. Because of. thesestrenuous fabricating operations, it is essential that the coatingapplied to the strip be uniform and of a minimum thickness so as toprovide proper protection. I If the coating is uneven or heavy, it willcrack, or lose its bond at the sharp ends so as to expose the metaltocorrosion.

, The thinner the coating is applied, the more economical is theoperation and the easier it is to make the necessary bends duringfabrication without undue stretching of the outer surface of thecoating, thus avoiding any break in the coatedsurface.

At the present time, all metal coating is done with roller coaters inwhich the rollers are of rather large diameter ranging from to ,14inches. These rollers usually have a resilient surface of some gelatineor rubber compound. Due

to the rather large diameter of the-rollers, there is a long surfacecontact between the roller and the metal surface, and the coatingcontacting the metal and the roller is gradually split as the rollerrevolves. For a roller 10 inches in diameter, this surface contact isalways at least one inch in length. Depending upon the viscosity and theamount of coating material applied, it has a tendency to gather instreaks as it approaches the breaking point. This results in rather highinch, the surface contact is reduced to a minimum ridges which runlongitudinally of the strip and may be spaced at distances from 3 5 ofan inch in low viscosity material. to A or of an inch in the heavier andmore viscous materials; these coating streaks or ridges not only destroyth protective value of the coating or final beauty or finish of thematerial, but obviously create an undesirable waste of coating material.j

In accordance with my invention, strip steel that is not flat and may betwisted, scalloped or burred, is coated with a thin and uniform layer ofthe desired coating material by applying an excess of the coating toone-or both sides thereof and then bending the strip transversely arts-n angle of from about 3 to 30.by breaking the strip over a bar of verysmall diameter which is positioned along the line ofthe bend and isconand the coating streaks or ridges referred to above are entirelyeliminated. I have found that with a $4; inch bar the surface contactdoes not exceed V8 inch, and in most cases the coating is split in adistance of a. of an inch beyond the line of contact. With such a shortrapid break, there is no noticeable streak formation.

The coating apparatus i5 comprises an upper resilient surface coatingroller 25 which receives coating material from a feed or distributingroller 26 and cooperating fountain roller 21, the latter of which isarranged to rotate in a bath 28 of the coating material. This uppersurface coater is of conventional construction and the setting of therollers 25, 28 and 21 is such that a layer of the coating material willbe applied upon the upper surface of the strip 5 as it passes beneathand in contact with the coatingroller 25. A supporting and guidingroller 30 is positioned on the lower side of the web or strip 6 betweenthe coating roller 25 and a second coating roller 3| which is suppliedwith coating material in the desired excess quantities by means of afountain roller 32 rotating in a bath 33 of the coating material. Thestrip 5 is shown as maintained in a substan.- tially horizontal positionin passing from the braking roller hi through the parts of the coatingapparatus thus far described and is thus coated on both sides thereofwith a slight excess of the coating material. All of the parts of thecoating apparatus are positioned as closely together as possible; andthe intermediate supporting roller is of extreme importance in insuringa suitable flat contact with the coating rollers 25 and 3| and inavoiding such twisting of the strip as would render the apparatusinoperative.

Upon passing beyond the coating roller 3|, the strip 5 is bent upwardlythrough an angle of from 3 to 30, depending primarily upon the thicknessthereof. In passing a web over such a bar, it will act to regulate thethickness of the coating material due to the provision of the grooves35; and the windings provide a, spiral surface which, when rotated,create a feeding action that serves to carry any undesirable foreignmatter over the edge of the strip where it may be caught in a suitablepan. However, when the wire 35 is omitted the bar still functionssatisfactorily but provides an even thinner layer. As mentioned above,it is the small diameter and resulting short surface contact which Ihave found to be particularly important in eliminating the undesirablestreaks and ridges in the applied coating.

. In the present instance, the bar 34 is mounted in a suitable bearing31 and provided at one end thereof with a driving gear or sprocket 38which may be connected up to any convenient source of 'powerso as torotate the bar 34 continuously during the coating operation. The bar isrotated in width of the strip which thus contacts the bar uniformlythroughout its width and accurately regulates and levels the coatingmaterial that has been applied to the upper surface of the strip 5 bythe coating roller 25. In any case, the tension provided by the feedandpull unit and the braking rollers should be suflicient to cause thestrip to be properly bent along a straight line in passing over the bar84. For strip steel of 0.010 inch thickness, this tension maybe about 50pounds per lineal inch of width of the strip. I

Similarly, the coating material applied to the lower part ,of the stripis regulated and leveled into a uniform layer free of streaks or ridgesby bending said strip back to a substantially horizontal plane, i. e.,bending it through an angle of from 3 to 30. This'is accomplished bybreaking the strip 5 over a small diameter bar t mounted for rotation ina suitable bearing ti. This second leveling bar performs the same actionon the coating material applied tothe lower side of the web and issubstantially identical in construction and operationwith the bar 3!.

With both sides of the strip 6 thus coated with a very thin and uniformlayer of coating material,

said strip is thus passed through the heater it,

where the coating, due to its uniformity and regulated thickness, isquickly and eifectively dried; and the strip may then be cooled andrewound as described above.

From the foregoing description, it will be understood that, by thepresent invention, I have provided an improved method and apparatus bymeans of which strip metal may be continuously coated on one orboth-sides with a thin and uniform layer of any desired coating materialfree from streaks or ridges and accurately regulated throughout theentire width'of the strip. Various changes may be made in theconstruction and method described and certain features or steps thereofmay be employed without others, without departing from my invention orof its advantages.

What I claim is:

1. A method-of continuously coating a side of a travelingstrip of metalwith a thin and uniform layer of a coating material, which comprisesmaintaining said strip under tension; covering one side of said stripwith an excess of the coating material; and bending said striptransversely through an angle of from 3 to 30 by breaking the strip anddrawing it over a small diameter bar with the coated side in contactwith said bar.

the amount of tension and the angle of bend being sumcient to cause saidstrip to become entirely fiat along the line of bend, so as to obtaincomplete contact between said strip and said bar throughout the width ofsaid strip, but insuflicient to cause a permanent deformation of saidstrip.

2. A method of continuously coating a side of a traveling strip of metalwith form layer of a coating material,

which comprises maintaining said strip under tension covering one sideof said strip with an excess of the coating material; and bending saidstrip transversely through an angle of from 3 to 30 b breaking the stripand drawing it over a bar rotating in the direction of movement of thestrip and having such asmall diameter that said strip has no greaterthan A; inch lineal surface contact therewith, the amount of tension andthe angle of bend being suflicient to cause said strip to becomeentirely flat along the line of bend, so as to obtain complete contactbetween said strip and said bar throughout the width of said strip, butinsuflicient to cause a permanent deformation of said strip.

3. A method of continuously coating both sides of a traveling strip ofsheet metal with a thin and uniform layer of a coating material, whichcomprises maintaining said strip under tension;

sacrificing any v sides of a thinand unip covering both sides of saidstrip with an excess of coating material; bending said striptransversely through an angle of from 3 to 30 by breaking the strip anddrawing it over a small diameter bar with one surface thereof incontactwith said bar; and bending said strip transversely through an angleoffrom 3 to 30 by breaking the strip and drawing it over a small diameterbar with the other surface in contact with said bar, the amount oftension and the angle of bend in each instance being suiiicient to causesaid strip to become entirely fiat along the line of bend, so as toobtain complete contact between said strip and said bar throughout thewidth of said strip, but insuflicient to cause a permanent deformationof saidstrip.

4. A method of continuously coating 9, side of a traveling strip ofmetal with a thin and uniform layer of a coating material, whichcomprises maintaining said strip under tension; covering one side ofsaid strip with an excess of the coat ing material; and bending saidstrip transversely through a predetermined angle by breaking the stripand drawing it over a small diameter bar with the coated side in contactwith said bar,

the amount of tension and the angle of bend being suificient to causesaid strip to become entirely flat along the line of bend, so as toobtain complete contact between said strip and said bar throughout thewidth of said strip, but insuillcient other side of said strip with anexcess of thecoating material; a first bar of from 1%; to posed in thepath of said strip so that one side will contact therewith; a secondregulating'and leveling bar of from s to of an inch in diameter arrangedbeyond said bar so that the other side of said strip will contacttherewith, the arrangement of said bars being such that said stripregulating and leveling will be'bent through an angle of from 3 to 30-in passing over each of them; and means arranged between said coveringmeans for sup-. porting said strip in its traveling movement betweenthem.

6. Apparatus for continuously coating both a traveling strip of sheetmetal with a thin and uniform layer of a coating material, whichcomprises meansior maintaining said strip under tension in its travelingmovement, said .of {*1 inch in diameter dis- 4- asssper tension beingequivalent to a tension of 50 pounds per lineal inch of width for ametal strip 0.010

inch thick; means for covering one side of said strip with an excess ofthe coating material; means tor covering the other side of said stripwith an excess of the coatingmaterial; a first regulating and levelingbar of from f to of an inch in diameter disposed in the path of saidstrip so that one side will contact therewith; a

second regulating and leveling bar of from v to of an inch in diameterarranged beyond

